This invention pertains to the art of diesel engines generally, and in particular to protective arrangements for diesel engine glow plugs.
Many diesel engines are provided with glow plugs which are particularly useful in cold weather to aid in starting the diesel engine. One typical protection arrangement is to connect the glow plugs in parallel and in series with a single fuse link.
It has been the experience of the assignee of this invention that, in connection with its product, i.e., transport refrigeration units using diesel engine prime movers, some operators of the units will use a remote power source to aid in obtaining a start in severely cold weather. Sometimes a twelve volt battery will be connected in series with the twelve volt battery for the engine. At other times a remote starter-generator may be connected to the glow plug circuit and, depending upon the setting of the starter-generator, significantly greater voltage than the nominal twelve volts may be applied to the glow plugs. The application of the voltages higher than the nominal twelve volts may result in fuse link burnout or, alternatively and sometimes more seriously, enlargement of the tip or tips of one or more glow plugs. The reason the enlargement of the glow plug tip may be more serious than the burnout of a fuse link is that the tip of the glow plug may enlarge to a degree that the plug may not be able to be removed from the engine without stripping off the end of the glow plug and the engine head must then be removed to extract the particle(s).
It is the aim of this invention to provide an arrangement to prevent enlargement of glow plug tips under a condition of either an overvoltage being applied to the glow plugs, or under a nominal voltage condition.
The invention is premised in part upon the observation that ordinarily a glow plug blowout follows a short in the glow plug tip. The time period between the shorting of a glow plug tip and its enlargement will vary in accordance with a number of factors or conditions. By relatively quickly interrupting the circuit to the shorted glow plug, as in a fraction of a second, glow plug tip enlargement can be prevented.